Field of the Invention
This invention relates to offset voltage elimination, especially to a random chopper control circuit.
Description of the Related Art
In general, in a LCD panel driving system, gate drivers and source drivers are necessary to control pixels of the LCD panel. The gate drivers are used to control gates of the pixels of the LCD panel switched on or off; the source drivers are used to provide driving voltages to corresponding pixels of the LCD panel. For a LCD apparatus, a lot of source drivers are necessary to provide driving voltages to all pixels of the LCD panel, and each source driver usually includes hundreds of buffers to provide driving voltages to different pixels respectively.
Because there will be differences in the manufacturing process, each buffer will have its own offset voltage. A chopper stabilization method and an auto-zeroing method are usually used to eliminate the offset voltage.
As to the chopper stabilization method, the offset voltage can be eliminated in space and in time. For the elimination in space, the offset voltage of each pixel can be eliminated by adjacent pixels. For the elimination in time, each pixel has an offset voltage when it displays a frame and the offset voltage can be eliminated by itself when it displays another frame next to the frame.
In the conventional chopper algorithm, a chopper control signal is designed to perform changes line by line or frame by frame in a regular arranging order. Please refer to FIG. 1, a frame control signal YDIO is used to indicate the start of each frame; a line control signal STB is used to indicate the start of each line; a first chopper control signal CH1˜a third chopper control signal CH3 are used to control the switching of the exchange unit of the amplifier in different arranging orders respectively to realize offset voltage elimination.
For example, as to the first chopper control signal CH1, as shown in FIG. 1, the first chopper control signal CH1 has a regular arranging order (1F1L) of +, −, +, −, +, − for the N-th frame and −, +, −, +, −, + for the (N+1)-th frame.
As shown in FIG. 2, the first chopper control signal CH1 performs voltage offset on the green pixel G of the first frame F1 line by line from the first line L1 to the sixteenth line L16 through its regular arranging order (1F1L) of +, −, +, −, +, −, +, −, +, −, +, −, +, −, +, −, wherein + represents positive voltage offset and − represents negative voltage offset. Then, the first chopper control signal CH1 performs voltage offset on the green pixel G of the second frame F2 line by line from the first line L1 to the sixteenth line L16 through its regular arranging order (1F1L) of −, +, −, +, −, +, −, +, −, +, −, +, −, +, −, +. As to the third frame F3 and the fourth frame F4, they can be referred to the above-mentioned first frame F1 and second frame F2.
However, in some specific display applications, since the offset voltage elimination in time is limited by the low frame rate, the LCD panel will appear flicker phenomenon. In addition, in some specific panel structure, some “Killer Patterns” fail to eliminate the offset voltage in space. The above-mentioned conditions will cause the failure of the chopper stabilization method and the offset voltage elimination cannot be eliminated successfully.
Therefore, the invention provides a random chopper control circuit to solve the above-mentioned problems.